U.S. patent application Ser. No. 08/001,007 filed on Jan. 5, 1993 discloses an adapter that displays text data as an accompaniment to audio programs such as songs, speech, or foreign language dialog. The adapter is designed to be connected to the audio output socket of a cassette tape player that operates a cassette tape on which text data and audio programs are recorded. The text data is encoded on the tape so it lies within the audio frequency range, for example, as dual tone multi-frequency (DTFM) signals. As the tape player operates, the adapter decodes and displays the text data and transmits the audio programs to an audio output socket. The described adapter has application in karaoke, language instruction, and other environments where reproduction of an audio program is to be accompanied by a real time text display synchronized to the program.
There are stringent limitations on the rate of text data that can be transmitted in the audio frequency range by a cassette tape. These limitations may make it difficult to synchronize the display of text data with an audio program.
If the text data is to be displayed in a symbolic language such as Chinese, rather than an alphabetic language, a dramatic increase in memory capacity of the adapter is needed to store the library of dot patterns required to generate all the characters.